Information that could be accessed did not include posts, messages or telephone numbers, a spokesperson said.

Privacy pressure

Google did not specify how long the software flaw existed, or why it waited to disclose it.

The Wall Street Journal reported that Google executives opted against notifying users earlier because of concerns it would catch the attention of regulators and draw comparisons to a data privacy scandal at Facebook.

Earlier this year, Facebook acknowledged that tens of millions of users had personal data hijacked by Cambridge Analytica, a political firm working for Donald Trump in 2016.

"Every year, we send millions of notifications to users about privacy and security bugs and issues," a Google spokesman told AFP.

"Whenever user data may have been affected, we go beyond our legal requirements and apply several criteria focused on our users in determining whether to provide notice."

The company said it determined its course of action based on the data involved in the breach, lack of evidence of misuse and challenges in accurately determining which users to inform.

Google will wind down Google+ during the coming 10 months to allow people time to download pictures, videos or other data they want from their accounts.

Meanwhile, Google planned to add new workplace-oriented features to enhance the appeal of Google+ as a "secure corporate social network" to be used inside business operations.

"We have many enterprise customers who are finding great value in using Google+ within their companies," the internet firm said.

"Our review showed that Google+ is better suited as an enterprise product where co-workers can engage in internal discussions."

Phones and email

As a result of the security audit, Google plans to allow users to more tightly control what data is available to applications that sync with Google accounts or its free Gmail email service.

"Going forward, consumers will get more fine-grained control over what account data they choose to share with each app," Google said.

Applications tailored to augment Gmail will also face new rules regarding data handling and be subject to security assessments, according to the company.

Applications for use on Android-powered smartphones that seek phone or SMS data will need to conform to stricter rules when it comes to calls or text messaging, Google said.